Salicylic Acid Enhances Biocontrol Efficacy of the Antagonist Cryptococcus laurentii in Apple Fruit

Abstract

Biological control and induced resistance are two of the promising approaches to the control of postharvest diseases. This study was conducted to evaluate the efficacy of salicylic acid (SA) alone or in combination with an antagonistic yeast, Cryptococcus laurentii, in controlling the blue mold disease caused by Penicillium expansum on apple fruit wounds. SA alone significantly inhibited the spore germination of P. expansum in vitro when its concentration was increased to 1000 μg ml−1, but it was not effective in controlling the disease in vivo. Simultaneous application of SA and C. laurentii to the wounds on the apple fruit surface showed that SA could improve the efficacy of C. laurentii against P. expansum in a concentration-dependent manner, being most effective at 10 μg ml−1 but less effective at a higher or lower concentrations. Besides reducing the blue mold incidence in the local wound sites, the combination of C. laurentii with SA at 10 μg ml−1 also had a synergistic effect on the induction of fruit resistance to the disease, which might be associated with a rapid increase in peroxidase, phenylalanineamonialyase and lipoxygenase activities. In addition, SA at 100 μg ml−1 or above showed an adverse effect on the growth of C. laurentii in vitro and in vivo, whereas it had no effect when its concentration was decreased to 10 μg ml−1 or lower. This suggested that SA could enhance the biological activity of C. laurentii in apple fruit by inducing resistance to pathogens based on the antagonistic activity of C. laurentii.